Need information on SES P0171 [Archive] - GrandAmGT.com Forum

PDA

View Full Version : Need information on SES P0171


destroyer179
08-01-2012, 02:45 PM
On my way back from the post office today the SES popped on. Autozone told me that it was code P0171 and that it could be either an 02 sensor, a fuel injector problem or an ignition misfire-repair. It doesn't seem to run much different than it used to, though it does seem to pulse a little at idle. I had asked about the idling question almost a week ago on here and ended up replacing a leaky egr valve and two cracked vacuum hoses which improved it. Anyone else have experience with this code?

chris_gt_74
08-01-2012, 04:43 PM
This just a copy and paste from a quick Google search.

A code P0171 may mean that one or more of the following has happened:
•The MAF (Mass Air Flow) Sensor is dirty or faulty
•There could be a vacuum leak downstream of the MAF sensor
•Possible cracked vacuum or PCV line/connection
•Faulty or stuck open PCV valve
•Failed or faulty oxygen sensor (bank 1, sensor 1)
•Sticking/plugged or failed fuel injector
•Low fuel pressure (possible plugged/dirty fuel filter!)
•Exhaust leak between engine and first oxygen sensor

AaronGTR
08-01-2012, 10:14 PM
DTC P0171 is for "Fuel Trim System Lean". The cars computer reads the O2 sensor, and adjusts fuel trim based on the reading, either rich or lean. If it reads lean, it adds fuel. The fuel trim can only add a maximum of 22% though. If the average long term fuel trim is over 21% it sets the DTC. This basically means you are not getting enough fuel. A misfire would not cause this code to set, however it could cause a misfire. If you were getting a misfire though it would set a code. It also will normally set a code if there is a problem with the MAF sensor.

How many miles are on your car? The O2 sensors only last for 100k miles, sometimes less. If yours hasn't been replaced it could be bad. Also the fuel filter should be changed every 30k miles. A plugged filter could cause low fuel pressure which would lead to a lean condition.

Diagnostic info for this code in the service manual are, in order:

-Bad O2 sensor or damaged wiring.
-Poor PCM to engine grounds.
-Fuel system pressure low.
-Faulty fuel injector.
-Vacuum leak.
-Exhaust leak (could cause fresh air to enter the exhaust in front of the O2 sensor).
-Malfunctioning MAF sensor.
-Contaminated fuel.

destroyer179
08-01-2012, 10:55 PM
My car has 126k on it and as far as I know it has never had any sensors replaced. Also couldn't tell you when the last time the fuel filter was changed. Since I've owned it I've put 20k on it and never changed the filter.

AaronGTR
08-02-2012, 04:40 PM
No maintenance records with it huh?

Well it's probably safe to assume it hasn't been well taken care of then. First thing I would do is get a new O2 sensor and fuel filter, and see if that solves your problem. Hopefully that will do it, and it should increase your fuel mileage and HP too, bringing them back closer to factory levels.

Check the air filter while you are at it, and the spark plugs might also need to be replaced. They only last for 100k as well, and the serpentine belt too.

destroyer179
08-02-2012, 05:04 PM
No records sorry. I'm still friends with the guy I bought it from but he only owned it for about a year. Before that it was just some dude that neither of us are in contact with. I talked to my neighbor today also and let him listen to it (i just found out that he is a certified mechanic) and he told me also to take the time and pull the UIM off since I just changed it, check the gaskets for cracked areas and put on new gaskets. He said if they are cracked, put the new ones on and continue to test with the ported one. If they aren't cracked he said put new ones on and try the stock again. Your thoughts? I know he's certified but he still hasn't done nearly as much work with this type of car as you and as far as people on this board go you're kind of the like the engine guru.

No maintenance records with it huh?

Well it's probably safe to assume it hasn't been well taken care of then. First thing I would do is get a new O2 sensor and fuel filter, and see if that solves your problem. Hopefully that will do it, and it should increase your fuel mileage and HP too, bringing them back closer to factory levels.

Check the air filter while you are at it, and the spark plugs might also need to be replaced. They only last for 100k as well, and the serpentine belt too.

AaronGTR
08-02-2012, 08:14 PM
Haha, well I didn't know you just changed the UIM. That could be useful info. So you put a ported one on in place of the stock one? Did you change the intake gaskets, or re-use them? Sometimes you can get away with re-using them, but often they tear and you need to replace them. Same with the throttle body gasket.


I'd check out that other stuff I mentioned though first. If the O2 sensor and/or fuel filter have never been changed, it will run better after changing them, even if those don't solve your problem.

destroyer179
08-03-2012, 11:14 PM
I put new gaskets on when I switched it out. Is there a chance that I need to have someone reprogram the computer so that it knows what's going on? Would that make it idle poorly but still drive and accelerate smoothly as always? I also took the UIM back off last night and checked it with a bright light and straight edge, finding nowhere that shows light coming through, then put new gaskets again, and it still idles poorly. The SES went off though and I don't even have any pending codes when I plug in my scanner.

AaronGTR
08-04-2012, 10:18 AM
No, just changing the UIM won't affect anything enough that you would need PCM programming for it to run correctly. It should run the same as before. Some codes will turn the SES light off after a certain number of ignition cycles without seeing the problem, and will turn it on after seeing the problem for a certain number of consecutive cycles. Even if the code isn't active though, there should still be a history code stored. I don't know if your scanner has the ability to check history codes though. But anyway if you had the light come on once, and there is still an idle problem, then chances are there is still a problem and it will come back. Stop messing around with other things and go get an O2 sensor and fuel filter. ;) Chances are they need to be replaced anyway, and even if they don't solve the idle issue, the car will probably still run better and get better mileage, and it will be one more thing to check off the list. You need to eliminate possible problems so that you can narrow down the number of places to look.

destroyer179
08-04-2012, 04:54 PM
Aaaaaaand here's another thing that just happened: decided to check the code again and now in addition to the original I'm getting the P0300 misfire code. I have a new filter but didn't get around to doing it yet. Is there a way to test my ignition coils with a voltmeter or something to see if those might be giving me the second code?

destroyer179
08-11-2012, 03:33 AM
Well, after lots of diagnostics, testing tubes, sensors, and changing the fuel filter I have figured out the problem here. I had a relative tell me to take some starting fluid and spray it all around the intake to try and find if there was a vacuum leak. The bottom bolt of the throttle body seemed to have a leak around it and I ended up having to drill out that bolt hole and use helicoil in it. That sealed the leak and corrected the lean condition. Just wanted anyone that might care to know that I found the solution.